How are you deciding how quickly the transfer is occurring?
Note that the transfer speeds that you notice are limited by the slowest link in the chain between you and the server. If you are testing transfer rates by loading a page in your browser, you're probably being limited by whatever network speed you have available through cable/DSL/whatever.
If you notice that another website hosted at a server at the same data center is loading faster, then perhaps bandwidth isn't the trouble. Your browser could be rendering your page more slowly than it renders the other page.
For investigating the performance of your page, take a look at http://developer.yahoo.com/yslow/, there are other similar tools available.
Deciding on speed by when a page is rendering isn't a good technique. The content of the page affects the rendering time. There are a variety of ways to actually time the transfer, but again, that's probably telling you more about your Internet connection than your servers.